U.S. Pat. No. 6,304,693 issued Oct. 16, 2001 for Efficient Arrangement for Coupling Light from a Light Source to a Light Guide discloses a fiberoptic illumination system that efficiently couples light from a light source into a light pipe, or plurality of light pipes. The system may use a metal halide light source, a light collector comprising a coated hollow angle-to-area converter, and a single, coated quartz rod. The output of the preferred embodiment of this converter is not a circle, but two joined sections of a circle. Because of this, when a rod with a circular cross-section of equal or smaller area is placed in front of the light collector to couple light to the light pipes, not all of the light is collected. Only about 90% of the light is collected and delivered to one or more light pipes.
The single rod of the mentioned, prior art system has an output surface with a substantially even amount of illumination across its face, to allow a substantially equal amount of light to be delivered into each of several light pipes. The single rod has ultraviolet energy (UV) and infrared light (IR) filters on at least its input end to protect the light pipes, which are often made of plastic, and the rod thermally isolates the light pipe or pipes from the heat of the light source.
A disadvantage to using a single rod with a bundle of light pipes is that there are light losses due to the interstitial voids created at the interface of coupling multiple round light pipes to a single round rod. The present inventors have determined that the losses vary as the number of light pipes increase, but for four round light pipes of the same diameter, a maximum collection efficiency of typically about 72% is realized, for an overall efficiency of typically about 65% of collected light delivered into the light pipes.
It would thus be desirable to provide a fiberoptic illumination system that delivers a higher percentage of light from a light source into multiple light pipes.